"blowjobable" - a girl with the following characteristics:
-nice mouth/lips along with surrounding facial features
-somewhat shorter in height (mouth at a closer level to your dick)
-large captivating eyes (something to look at while she does her thing)
-fairly attractive body (something else to look at while she does her thing)
-crazy enough to be into that sort of thing but not so crazy that she might pose a danger to the very valuable object you are lending her mouth for the time being
-somewhat plain or cute-ish nose that is not so defined or unattractive that it takes attention off the eyes
-longer hair that offers the man the ability to guide the movement of the head
...or a guy that girls would give a blow job to.

Guy 1: "Wow! That girl has some really nice lips and beautiful eyes"
Guy 2: "Yeah, she's pretty blowjobable... I could totally see her sucking on my dick"